Variable-resistance unit



S. W. LAW.

VARIABLE RESISTANCE UNIT. 111 1 L1c1111o11 F1151) 11111.11. 1919.RENEwEn 11111111, 1921.

72m w, BFM w/ #rra/WYE 75 Patented Mar. 7 1922.

PATFJNT FFICE.

STANLEY IV. LAV?, ST, PAUL; IINNESOTA.

VARIABLE-RESISTANCE UNIT.

Application filed January I7-, 1319, Serial No. 27171. Renewed July l1,1921.

To all fr0/0m t may com-cm.'

Be it known that I, STANLEY TV, Law, a citizen of the United States,resident of Paul, county of Ramsey, State of li/linnesota, have inventedcertain new and useful Improvements in Variable-Resistance Units, ofLwhich the following is a specification.

The objectI of my invention is to improve theresistance block or unitshown and described in Letters Patent of the United States, No.1,142,586, issued to me June 8, 1915. In the useA of this invention Ihave discovered that a bolt-or discharge of lightning has a tendency tojump from the edge or corner of theconducting plate to the resistancewire and burn out the unit and my present invention obviates thisdiiiculty by so mounting the plate that there will be less distancebetween it and the adjacent terminal than between the plate and theresistance coil. The result is the high tension electric discharge willjump the narrow gap to the terminal rather than the wider gap to theresistance coil.

The invention consists generally in various constructions andcombinations, all as hereinafter described and particularly pointedoutin the claims.

In the accompanying drawings forming part of this specification,

Figure 1 is a plan view of a resistance unit embodying my invention,

Figure 2 is a longitudinal sectional view of the same,

Figure 3 is a sectional view on the line 3 3 0f Figure 2.

In the drawing, 2 represents a block of suitable insulating material,preferably porcelain wherein the terminals 3' and 4L are mounted in theusual way. Between these terminals the block is provided with a spiralgroove 5. A resistance wire 6 is attached at its end to the terminals 3and l in the usual way and is coiled in the groove 5 which. around theresistance wire is filled with a suitable insulating' material 7 so thatthe wire is thoroughly concealed and protected thereby; On the upperside of the bleek the resistance wire is provided with a series ofmetallic contacts 8 formed in any suitable way, preferably by droppingVsolder or like material on the coil. These contact surfaces arearrangedk preferably in rows, as indicated inFigure l, runninglengthwise of the Specification ci Letters Patent. Patented D131', 7,1922,

'serial No. 483,949.

block, the contacts of one row being in staggered relation to those ofthe other row and there being as many contact surfaces as there are'sections of the groove in the top of the block, although in Figure 1 Ihave shown one grooweI at the right hand end of the block with thecontact surface omitted from the wire section in that groove. Thesecontact surfaces project up through the insulating material 7 and areexposed on the upper surface of the block and the wire closes thecircuit between the terminals through these contacting surfaces. For thepin-pose of \,';fn'ying the effective length of the resistance wirethrough which the current is compelled to pass or in effectsliertcircuiting the resistance, I provide a plate 9 mounted on one ofthe terminals 3 and having an offset 10 formed therein near the terminalfor the purpose of raising that portion of the plate which overhangs theresistance wire a considerable distance therefrom to form a wider gap atthis point than shown in my patent above referred to, and at the sametime have the end of the plate that is mounted on the terminal the samedistance from the top of the block. This wide air gap between the plateand the coil reduces, of course, the tendency of an electric dischargeto jump from the plate to the wire. rllhe plate is provided with aseries of holes l1 in whicl a contacting screw 12 tappeoy and secured bysuitable means, such as a lock nut 13, the number of holes in the platecorresporidingl to the number of contact surfaces on the wire and bymoving the contact screw back and forth in the holes I am able teincrease or decrease the degree of resistance in the coil, reducing orincreasing the number of loops in the wire through which the current iscompelled to pass in flowing from one terminal to the other.

The end 14 of the plate 9 instead of being cut square across andterminating a considerable distance from the terminal as in my formerpatent, is made tapered and eX- tends to a point where there is only anarrow gap between it and the terminal, so that if a bolt of lightningenters the instrument, it will follow the shortest air gap and jump fromthe point of the end 14 to the terminal rather than from the plate tothe resistance wire andthis direction of fiow of the electric dischargeis made all the more probable by the tapered 'torni ot the end ot theplate; that is, the corners are cnt away which in my former `)atentovcrhung the resistance coil and a order a convenient path ior theelectric discharge to jump to the coil from the end of the plate.

These two ifeatures-the Vforming ot the conductor plate to raise itabo'vc the resistance coil and the 'tapered end ot the plateform thesubject matter' ot my present invention.

I prefer to provide a sott iron core l5 molded in the block 2 andencircled by the convolutions ot the coil. This core, which ispreferably in the form ot a solid iron rod, will greatly increase theimpedance ot the coil to the passage of a lightning discharge andthereby increase the efficiency ot the device for the purpose designed.

I claim as my invention:

1. A resistance unit comprising an insulating block and terminalsmounted thereon, a resistance wire in circuit with said terminals andcoiled around said block, a contact plate in circuit with one ot saidterminals and overhanging the coils ot said wire, means adjustablymounted on said contact plate for contacting with the convolutions ofsaid wire and said plate having a tapered end extending tol a point nearthe other terminal and having a narrower air gap between it and saidterminal than between said plate and the adjacent wire convolutions.

2. A resistance unit comprising an insulating block and terminalsmounted thereon, a resistance wire in circuit with said terminals andcoiled around said block, a contact plate in circuit with one ot saidterminals and overhanging the coils of said wire, means adjustablymounted on said contact plate for contacting with the convolutions ofsaid wire and said plate having one end extending to a point near theother terminal and having a narrower air gap between it and saidterminal than between said plate and the adjacent wire convolution.

3. A resistance unit comprisingr an insulating block and terminalsmounted thereon, said block having a spiral groove formed thereinbetween said terminals, a resistance wire in circuit with said terminalsand coiled around said block in said groove, and insulating materialwherein said wire is embedded in said groove, the convolutions of saidWire having contacting surfaces formed thereon exposed through saidinsulating material, a contact platev in circuit with one of saidterminals and overhanging said contacting surfaces and having a wide gapbetween them and a circuit closing device mounted on said plate andmovable thereon for engaging said contacting surfaces.

4p. A resistance unit comprising an insulating block and terminalsmounted thereon,

a resistance wire in circuit with said terminals and coiled around saidblock, a contact plate in circuit with one ot said terminalsI andoverhanging the convolutions'o said resistance wire and spacedtherefrom, said plate having an offset therein adjacent said terminalfor increasing the width of the air gap between said plate and said wireconvolutions, the end of said plate being adjacent the other terminal toprovide a narrowerI air gap between them than between said plate andwire convolutions, said wire having contacting surfaces formed thereonand a circuit closer mounted on said contact plate and movable thereonfor engaging said contacting surfaces.

5. A resistance unit comprising an insulating block and terminalsmounted thereon, a resistance wire in circuit with said terminals andcoiled on said block, a contact plate in circuit with one of saidterminals and cvcrhanging the coils of said wire and spaced therefrom.there being a narrower air gap formed between said contact plate and theother terminal than between said contact plate and the convolutions ofsaid coil, for the purpose specified.

6. A resistance unit comprising an insulating block and terminalsmounted thereon, a resistance wire in circuit with said terminals andcoiled on said block, a contact plate in circuit with one of saidterminals and overhanging the coils of said wire and spaced therefrom,there being a narrower air gap termed between said contact plate and theother terminal than between said contact plate and the convolutions ofsaid coil, and a sott iron core embedded in said block and encircled bythe convolutions of said resistance wire, for the purpose specified.

7. A resistance unit comprising an insulating block and terminalsmounted thereon, a resistance wire in circuit with said terminals andcoiled around said block, a contact plate in circuit with one of saidterminals and overhanging the coils of said wire, means mounted on saidcontact plate for contacting with the convolutions of said wire and saidplate having one end extending to a point near the other terminal andhaving a narrower air gap between it and said terminal than between saidplate and the adj acent wire convolution.

v8. A resistance unit comprising an insulating block and terminalsmounted thereon, a resistance wire in circuit with said terminals andcoiled around said block, means for establishing a circuit through oneof said terminals and the convolutions of said coil, said means beingmounted to direct a lightning discharge away from said coil and throughthe other terminal.

9. A resistance unit comprising an insulating block and terminalsmounted thereon, a resistancev wire in circuit with said terminals andcoiled on said block, means for short cil'cuiting said resistance Wirethrough one of said terminals and directing a lightning discharge intothe other terminal.

l0. A resistance unit comprising an insulating block and terminalsmounted thereon, a resistance Wire in circuit With said terminals andcoiled on said block, and means vfor diverting a lightning dischargefrom said resistance Wire to said terminals.

In Witness whereof, I have hereunto set my hand this 4th day ofSeptember, 1918.

STANLEY W. LAW.

